A construction machine, for example, a hydraulic excavator is provided with an engine and a hydraulic pump driven by the engine, and is torque-controlled such that an absorption torque of the hydraulic pump does not exceed an output torque from the engine. The construction machine is also provided with a hydraulic drive circuit to which pressure oil is fed from the hydraulic pump. This hydraulic drive circuit includes hydraulic equipment such as hydraulic actuators for a boom cylinder, arm cylinder and the like required to drive attachments such as a boom, arm and the like, or hydraulic actuators such as a swing motor and travel motor for driving a swing upperstructure and travel base; and also directional control valves for controlling operations of these hydraulic actuators. With respect to hydraulic excavators having such a construction, there is nowadays an increasing desire for the purification of exhaust gas emitted from engines.
As a conventional technology for purifying exhaust gas, there is the technology disclosed in Patent Document 1. Although this conventional technology is directed to an exhaust gas purification system for arrangement on an automobile different from a construction machine to which the present invention is directed, it includes an exhaust gas control means for performing treatment to purify, with a reducing agent such as urea, nitrogen oxides in exhaust gas emitted from an engine, a reducing agent solution reservoir for storing the reducing agent solution, such as urea aqueous solution, to be fed to the exhaust gas control means, and a liquid level sensor for detecting a remaining amount of the reducing agent solution stored in the reducing agent solution reservoir, that is, a remaining amount detection means. It also includes an alarm that is actuated to give a warning to a driver when the remaining amount of the reducing agent solution stored in the reducing agent solution reservoir has decreased to or below a predetermined amount.
This conventional technology is designed such that, when the remaining amount of the reducing agent solution has decreased to or below the predetermined amount, the alarm is actuated to give a warning to the driver as described above, and further, the engine is controlled at a low output by an engine control unit, and by these warning and control, a replenishment of the reducing agent solution is urged.
Patent Document 1: JP-A-2002-371831